A refrigerant circuit usually comprises a compressor, a condenser, an expansion valve and an evaporator. The expansion valve controls the flow of refrigerant from the condenser into the evaporator. This flow is controlled according to a demand of cooling power. This demand is detected by means of the bulb. The bulb comprises a chamber filled with a filling adapted to influence a valve element of said thermostatic expansion valve. When the temperature increases the pressure of this filling increases as well. A capillary connects the bulb to the thermostatic expansion valve so that the pressure of the filling propagates through the capillary towards the thermostatic expansion valve to influence the opening degree. When the temperature around the bulb decreases the pressure of the filling decreases as well and the thermostatic expansion valve is actuated in the opposite direction.
When such a thermostatic expansion valve shows a defect, the service people often have to replace it. This replacement requires that the service people have a suitable spare part with them. This requirement makes the service complicated since there is a large variety of different bulbs, one for each specific application. It is difficult for the service people to have all different types of combinations of bulbs and valve with them in their car.